cast literal to char * when assigning to input_line_ptr

cast literal to char * when assigning to input_line_ptr

various places either directly or indirectly set input_line_pointer to point at
a literal.  Currently lots of places modify the string input_line_pointer
points at, so making it const isn't easy.  Since most if not all of these
places assign to input_line_pointer to parse an expression it would probably be
best to add ways to generate and deal with expressions that doesn't involve
parsing strings, but for now adding some casts seems easiest.

gas/ChangeLog:

2016-03-31  Trevor Saunders  <tbsaunde+binutils@tbsaunde.org>

	* config/tc-i960.c (parse_expr): Cast to char * when assigning to
	input_line_pointer.
	* config/tc-m32r.c (expand_debug_syms): Likewise.
	* config/tc-msp430.c (msp430_dstoperand): Likewise.
	* config/tc-z80.c (md_begin): Likewise.
	* stabs.c (stabs_generate_asm_func): Likewise.